To block PDF or ZIP file attachments in Postfix, you can use the mime_header_checks option in the Postfix configuration file (main.cf).
The mime_header_checks option allows you to specify regular expressions that will be applied to the headers of email messages. If a message header matches a specified regular expression, the message can be rejected, discarded, or modified.
To block PDF or ZIP file attachments, you can use the following regular expression:
/^Content-Disposition:.*(pdf|zip)/ REJECT Blocked file type: $1
This regular expression will match any message with a Content-Disposition header that contains the strings pdf or zip, indicating that the message contains a PDF or ZIP file attachment. When a match is found, the message will be rejected with the specified error message.
To enable the mime_header_checks option, you can add the following line to the main.cf configuration file:
mime_header_checks = regexp:/etc/postfix/mime_header_checks
Then, create the mime_header_checks file in the /etc/postfix directory and add the regular expression above to the file.
After making these changes, you will need to reload the Postfix configuration to apply the changes. You can do this using the postfix reload command.
For more information about using the mime_header_checks option to block attachments in Postfix, you can refer to the Postfix documentation or search online for tutorials and examples.